8263017: Read barriers are missing in nmethod printing code

Reviewed-by: eosterlund, kvn

src/hotspot/share/code/nmethod.cpp

@@ -936,6 +936,8 @@ void nmethod::maybe_print_nmethod(DirectiveSet* directive) {
 }
 
 void nmethod::print_nmethod(bool printmethod) {
+  run_nmethod_entry_barrier(); // ensure all embedded OOPs are valid before printing
+
   ttyLocker ttyl;  // keep the following output all in one block
   if (xtty != NULL) {
     xtty->begin_head("print_nmethod");